Substrates in which a silicone-based release agent is coated onto the surface of a substrate such as a plastic film or paper are widely used as release films.
However, the aforementioned substrates are easily charged, and tend to become even more easily charged when coated with a silicone-based release agent. Consequently, there has been a need to impart antistatic properties to these release films.
Although ionic conductive compounds such as surfactants have been widely used in the past as antistatic agents, since the conductivity of ionic conductive compounds is dependent on humidity, the antistatic properties thereof are unstable, while also having the problem of bleeding out from release films. Therefore, use of π-conjugated electrically conductive polymers, in which electrical conductivity is not dependent on humidity and which do not cause bleed-out, as antistatic agents for imparting antistatic properties to release films is known.
π-conjugated electrically conductive polymers are substances that are insoluble and infusible, and cannot be applied to coating or extrusion lamination. Therefore, Patent Document 1 discloses a liquid dispersion of a π-conjugated electrically conductive polymer in which a polyanion is added as a dopant and surfactant.
However, higher definition levels have come to be required by displays in recent years, and further improvement of mounting speed has come to be required in the field of component mounting in particular. Consequently, there is a growing need for protective films used in optical applications and antistatic base materials used for electronic and electrical components.
In response to these needs, Patent Document 2 proposes a release film that uses an addition curing-type silicone emulsion and a release agent containing a thiophene-based electrically conductive polymer. However, adhesion property of emulsion-type silicone relative to a substrate is low. Since, a large amount of water is contained in the emulsion-type silicone, corrosion of the coating machine may occur. Therefore, there is a difficulty for the emulsion-type silicone to use in an antistatic release film.
An antistatic release film has been known, in which an antistatic layer containing metal nanoparticles and a π-conjugated electrically conductive polymer is laminated on a substrate and a release agent layer containing silicone resin is laminated on the antistatic layer.
However, in the case, the antistatic layer and the release agent layer are formed independently, and hence, a plurality of coating operation is required, which lead to increase production cost. In the case of using metal nanoparticles, haze of antistatic layer tends to be increased, which is unsuitable for optical use.
Silicone has low hydrophilicity, and hence, it hardly dissolves in aqueous dispersion containing a complex of a π-conjugated electrically conductive polymer and a polyanion. A non-aqueous electrically conductive dispersion is proposed instead of the aqueous dispersion.
As the non-aqueous electrically conductive dispersion, organic solvent solution of polyaniline is disclosed in Patent Document 3.
In Patent Documents 4 to 6, an organic solvent dispersion is disclosed, in which the water contained in the aqueous dispersion containing a π-conjugated electrically conductive polymer and a polyanion is changed to an organic solvent.
In Patent Document 7, an organic solvent dispersion is disclosed, which is prepared by freeze-drying aqueous dispersion containing a π-conjugated electrically conductive polymer and a polyanion, and dissolving the residue in an organic solvent.